A microchip or a device called μTAS (Micro Total Analysis Systems) is in practical use, in which a micro flow path and a circuit are formed on a silicon or a glass substrate using a micro forming technology, so as to perform chemical reaction, isolation or analysis of liquid reagents such as nucleic acid, protein and blood in a micro space. Advantages of such microchip are to reduce amounts of samples and regents to be used and an emission amount of waste fluid, thereby realizing an economical system which is portable and space saving.
The microchip is manufactured by bonding two members wherein at least one of the two members has been subject to micro forming. Conventionally, a glass substrate is used for the microchip and various micro forming methods have been suggested. However, the glass substrate is not suitable for mass production, since it is extremely expansive, thus development of a disposable and low-cost microchip formed by a resin is desired.
The resin microchip is formed by bonding a resin microchip substrate having a surface on which a flow path channel is formed and a resin microchip substrate to serve as a cover of the flow path channel in a way that the surface on which the flow path channel is formed faces inside.
As the method of bonding the microchip substrate, there are cited a bonding method using an adhesive, a bonding method to meld the surfaces of the resin by an organic solvent (for example, Patent Document 1), a bonding method using ultrasonic wave welding (for example, Patent Document 2), a bonding method using thermocompression (for example, Patent Document 3) and a bonding method using laser (for example, Patent document 4).
For an element such as the microchip having a micro flow path through which liquid flows so as to perform examination, the flow path has been subject to a functional process. As the functional process, for example, a process to provide a hydrophilic property to the surface of the flow path is carried out so that the flow path does not absorb protein and so forth. For example, coating with a SiO2 film possesses a sufficient hydrophilic property, being characterized by high transparency and stability because of an inorganic material. Also, a film using a fluorine series resin to acquire a water-repellent property against a liquid reagent and a function to selectively absorb molecule is an example of the functional film.
As processes to acquire the functionality such as the hydrophilic property on the flow path surface, coating with organic or inorganic substance and a dipping by flowing a solution inside the flow path are cited. Among the above methods, functional film forming by CVD or by sputtering realizes the film having a sufficient functionality effect and adhesiveness in respect to the flow path surface as well as uniformity of the film depending on kind of the film.
Meanwhile, since the width of the micro flow path is several μm, it is difficult to form the functional film only on the inner surface of the flow path channel by masking on the microchip substrate. In particular, in case a pattern of the flow path channel formed on the surface is complicated, forming of the functional film by patterning so that the position of the pattern coincides is difficult. Thus, in the past the functionally film has been formed on an entire surface including the flow path channel with respect to the resin microchip substrate having a surface on which the flow path channel has been formed, thereafter the resin microchip substrate has been bonded with the resin microchip substrate to be a counter part with the surface on which the flow path channel faced inside, whereby the resin microchip has been manufactured.
However, in case the functionally film is formed on the entire surface including the flow path channel, the functional film is formed also on the bonding surface to be bonded with the microchip substrate representing the counter part and since the resins do not contact each other at the bonding surfaces, bonding of microchip substrates becomes very difficult.
Namely, in case the functional film is not formed on the resin microchip substrate, the microchip substrates can be bonded through ultrasonic wave welding, thermocompression welding or laser welding. In any of the above methods, resin surfaces of the substrates are melted and cured again so as to bond the resin microchip substrates one another. However, in case the functional film exists on the bonding surfaces, bonding of the microchip substrates becomes difficult.
Conventionally, as a method to form the SiO2 film on the inner surface of the flow path formed on the microchip, the SiO2 film is formed inner surface of the flow path by flowing a silicofluoride hydroacid solution into the flow path. (For example Patent document 5).
Patent Document 1: Unexamined Japanese Patent Application Publication No. 2005-80569
Patent document 2: Unexamined Japanese Patent Application Publication No. 2005-77239
Patent document 3: Unexamined Japanese Patent Application Publication No. 2005-77218
Patent document 4: Unexamined Japanese Patent Application Publication No. 2005-74796
Patent document 5: Unexamined Japanese Patent Application Publication No. 2002-139419